1. Field of the Invention
The present invention relates to a display device, and more particularly to a technique of conducting a displaying process with high brightness and excellent contrast.
2. Description of the Related Art
In the related art, as a display device which displays characters, an image, and other information, known are devices such as: a liquid crystal display device in which a liquid crystal display element and polarization plates are combinedly used, and orientations of liquid crystal molecules are controlled by applying a voltage to display an image; an organic EL display device in which an organic compound that becomes self-luminous in response to application of a voltage is used for displaying an image; and an electrophoretic display device in which a colored medium is placed between electrodes, and the colored medium is electrophoresed by application of a voltage to be moved toward one of the electrodes, thereby displaying an image.
As a technique which is not used in a display device, and in which light is modulation-controlled by a fluid, a waveguide which switches light by means of movement of a liquid is known (for example, see JP-A-10-333062 and JP-A-2001-201701)
In a liquid crystal display device which uses the polarization principle, a backlight of a large amount of light is required in order to obtain sufficient white brightness. In the case where polarization plates are placed in a crossed Nicols state (black-display state), slight light leakage occurs so that complete black is not attained in the black-display and the contrast is lowered. A liquid crystal display device has further disadvantages that it shows a viewing angle dependence and is poor in visibility in an oblique direction, and that components such as a driving circuit formed on the display face do not transmit light and hence the aperture ratio is low.
In an organic EL display device, the amount of emitted light depends on the material. Therefore, it is necessary to develop a material which is sufficiently bright. However, the development involves many difficulties. Furthermore, an organic EL display device has problems such as that the amount of light is remarkably reduced by deterioration of a material and an image is unevenly displayed depending on the place.
An electrophoretic display device has problems in that a gradation display cannot be sufficiently performed, that a transmission display is principally disabled, and that the performance is lowered by aggregation of electrophoretic particles to cause a problem in durability.
These display devices cannot be used without difficulty for a display purpose in which an even image must be displayed at high brightness and high contrast. In the present circumstances, therefore, it is requested to develop a display device which can perform a high-quality display meeting such a display purpose.
With respect to the above-mentioned waveguide serving as a light modulating element which switches light, only the configuration of a single element for an optical communication apparatus is disclosed. The modulating function is directed only to a process of controlling light reflection by the refractive index of the liquid. The waveguide cannot be directly used as a display device of the transmission type or the reflection type.